How to test an uninstalled temp gauge? '70 C10

[mosel70]

I have a 1970 C10 with factory gauges. Temp gauge hasn't worked since I've had the truck. Sensor and wiring are good. I have a new gauge on order. Is there a way to test the gauge before installing it?

https://www.brotherstrucks.com/67-72...tinfo/TMG1001/

[randy500]

I don't recall which value is what but the gauge input is 0-90 ohms from the sending unit, same as fuel sending unit, it you have an old fuel sending unit you could hook that up to test the gauge.

[Steeveedee]

IIRC, the instruments use 3 Volts. Do you have a Chassis Service Manual? I do, but for a '72, though I think that the gauges are the same in that range of years. I'll take a look at it tomorrow, if you don't have an answer before that.

[VetteVet]

Both the fuel gauge and the temperature gauge use the same 12 volt source from the fuse panel, cluster feed fuse, to pin 3 of the cluster plug.

Here is a diagram to illustrate.



It is shown as a purple wire here but it is actually a copper strip on the circuit board.

Have you grounded the sending unit wire with the key on to see if the gauge goes to full hot?

If you're getting no movement on the temp gauge, check the connection on pin six on the cluster plug and the sending terminal on the temp gauge for continuity with pin six.

I believe a check can be done on the new gauge using a nine volt battery and three jumper wires.
1. connect the positive terminal of the battery to the positive side of the gauge.

2. connect the negative on the battery to the body of the gauge.

3. jump from the sending terminal of the gauge to the body of the gaige and watch for movement of the needle toward full hot.

This should simulate the gauge being installed in the cluster with the key on and grounding the sending unit wire.
The nine volt battery will not damage the gauge.

I have not personally done this but it seems that it would work.
If you wanted to test various temperature settings on the gauge you would need a variable resistor, (potentiometer), in series with the sending unit terminal to the gauge body.